1. Field of the Invention
The present invention relates to a semiconductor module, and more specifically, relates to a structure for connecting a power device chip and an external electrode.
2. Description of the Background Art
A technique called wire bonding has been employed since 1980s as means of taking current out of a power device (see Japanese Patent Application Laid-Open No. 2010-238892). In the wire bonding technique, an electrode part of the power device and an external electrode are connected by using a thin aluminum or gold wire. However, this technique shortens the life span of a joint part formed by wire bonding due to heat stress generated by turning the power device on and off repeatedly. So, the maximum junction temperature should be set low if increase of a life span is given higher priority, resulting in the size increase or cost increase of a power module.
In response, direct lead bonding (DLB) technique has been suggested that is intended to enhance the reliability of a joint part. In the DLB technique, a lead frame is directly connected to an electrode part of an element on a surface of the element.
Further, transfer molding technique has been employed as a technique of sealing a power device (see Japanese Patent Application Laid-Open No. 2011-103367). For molding by the transfer molding technique, heated and pressurized resin is injected into a closed mold.
While enhancing the reliability of a joint part, the DLB technique entails higher cost than the wire bonding technique.
Further, sealing of a power device using the transfer molding technique achieves excellent reliability and excellent productivity. However, the transfer molding technique involves a large amount of initial investment to prepare a mold, for example, placing limitations on the degree of freedom of a terminal shape or dimensions. So, applying the transfer molding technique to a product group of a wide variety of types, or to a small group of products causes a problem of cost increase.